Our recent studies on autoimmune ovarian disease (AOD) have accrued evidence that stimulation by antigen and environmental factor early in life predisposes genetically-susceptible mice to early- and late-onset autoimmune disease, and this is explicable by the relative paucity of the CD4+CD25+ regulatory T cells present early in life. We have now made a new and striking observation that further strengthens the paradigm. Autoantibody (autoAb) to the ovarian zonapellucida 3 (ZP3) B cell epitope (335-342) was found to preferentially injure ovaries in neonatal mice while sparing ovaries of adult mice. Interestingly, although the ovarian disease is triggered by ZP3 autoAb, disease expression depends on the presence of T cells in the neonate, and is associated with de novo neonatal autoimmune T cell response to ovarian antigen. In addition, induction of this neonatal AOD is B cell epitope-specific; thus autoAb to a second ZP3 native B cell epitope (171-180) is non-pathogenic. Even more exciting, neonatal AOD develops only when the autoAb first reaches the neonatal mice in the first 5 days of life. Therefore, maternal autoAb can trigger in neonates pathogenic autoimmune T cell response and neonatal AOD; the disease induction is B cell epitope-specific, and only impacts neonatal mice that are known to be deficient in regulatory T cells. We now propose the following experimental approaches to further investigate these new and exciting observations. First, we will test the hypothesis that neonatal AOD is triggered by epitope-specific autoAb, which forms immune complexes with endogenous Ag, to induce ZP3 specific pathogenic T cell response and tong-term autoimmune memory. Second, we will test the hypothesis that activation of antigen presenting cells by immune complex is dependent on their Fc receptor, and this event is required for neonatal AOD induction. Third, we will test the hypothesis that CD4+ CD25+ regulatory T cell deficiency in neonatal mice explains the propensity of neonatal mice to develop autoimmune response and disease. This proposal will therefore address fundamental mechanisms responsible for autoimmune induction and prevention, and specifically, neonatal autoimmune diseases including systemic lupus-related congenital heart block.